In the past, the antisense method and the ribozyme method were known as means of repressing the transcription of organisms' genes to mRNA or repressing the expression of such genes. Research on the application of these techniques to, for example, repression of the expression of genes that can cause diseases, such as oncogenes, or improvement of plants, has made progress. In the antisense method, antisense DNA or RNA that is complementary to a specific site of a target gene, transcription of which is to be repressed, or mRNA to which the target gene has been transcribed, is employed. Existing antisense DNA or RNA, however, cannot be used for repressing the expression of genes other than the aforementioned target gene. Thus, new antisense DNA or RNA needs to be prepared in accordance with sequences of other target genes. In the case of the ribozyme method, the target DNA or mRNA cannot be cleaved with a ribozyme unless such ribozyme is designed to have a complementary sequence in order to bind to the target DNA or mRNA and to be capable of cleaving it at a predetermined position. Even when the ribozyme is designed to cleave the target gene, an excessive sequence is sometimes added to a transcribed ribozyme, which may result in the loss of ribozyme activity when, for example, it is ligated to a promoter such as the cauliflower mosaic virus 35S promoter and a transcription terminator sequence to construct a vector for introduction, and the resultant is actually introduced to a plant cell. In these conventional techniques, identification of the target gene and determination of its nucleotide sequence have always been indispensable. A method for repressing the gene expression via the gene knock-out technique has also been available, although this technique could not be applied to, for example, amphidiploid plants.
The present inventors have found that Arabidopsis proteins, namely, AtERF3, AtERF4, AtERF7, and AtERF8 are transcription factors which can significantly repress transcription of genes via an approach completely different from those of the aforementioned conventional techniques. They constructed effector plasmids comprising the genes encoding the aforementioned proteins and DNAs cleaved therefrom, and they introduced the resultants to plant cells. Thus, they actually succeeded in repressing gene transcription (JP Patent Publication (Kokai) Nos. 2001-269177 A, 2001-269178 A, 2001-292776 A, and 2001-292777 A). Further, the present inventors subjected a gene encoding tobacco ethylene responsive element binding factor (ERF) 3, which is a Class II ERF genes (JP Patent Publication (Kokai) No. 2001-269176 A), a gene encoding Oryza sativa Os ERF3 protein (JP Patent Publication (Kokai) No. 2001-269179 A), and genes encoding Arabidopsis thaliana ZAT10 and ZAT11, which are Zn finger protein genes, to a test similar to the aforementioned test. As a result, they found that transcription of target gene was repressed. They demonstrated the existence of a conserved motif (L/F)DLN(L/F)(X)P (X denotes any amino acid residue) (SEQ ID NO: 122) in proteins or peptides encoded by these genes, although the nucleotide sequences of these genes are different from each other (The Plant Cell, Vol. 13, 1959-1968, August, 2001).
An object of the present invention is to provide a simple and extensively applicable means for repressing transcription of genes, which eliminates the need for designing new DNA or RNA in each case in accordance with the nucleotide sequence of the target gene, unlike the conventional antisense and ribozyme methods. It is another object of the present invention to provide a peptide for facilitating the repression of transcription of genes and a gene thereof by further advancing the research concerning the transcriptional regulatory protein and identifying the most essential amino acid partial sequence that is actually needed for repressing transcription of genes.